CARDIAC is an educational tool developed at Bell Labs in 1968 to demonstrate the operating principles of computers. Made out of cardboard, users performed computations by hand using pencils. CARDIAC has 100 cells of random access memory (labelled 00 to 99), and it uses a 10-instruction instruction set. Each memory cell can hold a decimal integer between -999 and +999, and each 3-dight number 000 to 999 is a valid instruction; the leftmost digit is the instruction opcode, and the remaining 2 digits (the operand) indicate a memory address.

The simulator below demonstrates how CARDIAC works. Example programs can be selected from a dropdox listbox and executed by pressing the "Run" button. Users can also write, load, and run programs written in CARDIAC's machine or assembly language. A guide provides more information on the structure of CARDIAC and its programs.